Essentially every metal-working shop includes a parts cleaning station for cleaning metal parts of grease, oil,and dirt. A typical station consists of a metal sink having a hinged safety cover and a drain. The sink sits on top of a reservoir which may be a 55, 30, or 16 gallon drum. The drum contains mineral spirits. A pump, which is immersed in the mineral spirits, pumps it through a hose to a spray nozzle, which is used to spray the part. The dirt-laden fluid then drains back into the drum. The heavy dirt particles settle to the bottom of the drum and the mineral spirits are constantly recirculated.
Approximately once a month a truck picks up the residual solvent, takes it away for recycling, and replaces it with clean solvent. The used solvent may be taken to a distillation center for recycling back to its original state. Often, however, it is merely sold for its fuel value and the heavy residues are disposed of as hazardous materials waste.